QUATERNARY DEPOSITS NEAR THE SAN EMIGDIO MOUNTAINS, CALIFORNIA: EVIDENCE FOR A PALEOLANDSCAPE?
By: Paul G. Lavelle
Dr. Antonio F. Garcia Advisor
Earth and Soil Sciences Department California Polytechnic State University San Luis Obispo 2006 QUATERNARY DEPOSITS NEAR THE SAN EMIGDIO MOUNTAINS, CALIFORNIA: EVIDENCE FOR A PALEOLANDSCAPE?
Paul G. Lavell e
November 2006
ABSTRACT
Discontinuous low-relief surfaces are scattered throughout relatively high topography within the San Emigdio Mountains, California. These surfaces are considered anomalous, as they are preserved in a dissected, mountainous region that is affected by ongoing orogeny. Previous research has suggested that the low-relief surfaces may represent a once-contiguous alluvial surface. This project utilizes field mapping and scdimentological analysis to determine if the surfaces represent a paleo landscape. What is apparent from field work is the presence of two morphologically distinct lithologie units that most likely represent surficial geologic components of the same relict landscape. Acknowledgments
I would like to thank Dr. Tony Garcia for all of his generous help and support throughout my career at Ca l Poly. Dr. Garcia’s teaching efforts have been inspirational.
I would also like to thank Trisha, and my parents Robert and Deborah, for always being there for me. Approval Page
TITLE: Quaternary deposits near the San Emigdio Mountains, California: evidence for a paleolandscape?
AUTHOR: Paul G. Lavelle
DATE SUBMITTED: December, 2006
Dr. Antonio F. Garcia Senior Project Advisor Signature
Dr. Brent Hallock Department Chair Signature
iii TABLE OF CONTENTS
ABSTRACT...... i
ACKNOWLEDGMENTS...... ii
APPROVAL PAGE...... iii
TABLE OF CONTENTS...... iv
LIST OF FIGURES...... v
LIST OF TABLES...... vi
INTRODUCTION...... 1
REGIONAL GEOLOGY AND TECTONICS...... 2
MATERIALS AND METHODS...... 4
RESULTS...... 6
DISCUSSION...... 9
CONCLUSIONS...... I I
REFERENCES...... 13
APPENDICES...... 14
A. Figures ...... 14 B. Sedimentological descriptions of map units ...... 17 C. Tables ...... 19 D. Surficial geologic map of the Apache Saddle / Bitter Creek environs, San Emigdio Mountains, Kern and Ventura Counties, California ...... 20 LIST OF FIGURES
Site Map...... 14
Low Relief Surface (photograph) ...... 15
Low Relief Surface (photograph) ...... 15
Exposure of map unit Qcf (photograph) ...... 16
Exposure of map unit Qaf (photograph)...... 16
v LIST OF TABLES
1. Field criteria for distinguishing facies types on alluvial fans Introduction
This study focuses on prominent low-relief surfaces preserved above 900m near the San Emigdio
Mountains. California, field observations and data collected will comprise one phase of
a larger-scope investigation evaluating the influence of climate, erosion and tectonics in a region affected by Quaternary upli ft. Hypsometric analysis of the study area has shown evidence for a
once contiguous low-relief alluvial surface (Dean, 2005). If the alluvial deposits comprising the
surface represent parts of a paleolandscape, they may convey information regarding geomorphic
processes. Similar plateau-like surfaces have been used in previous studies to deduce climate-
erosion-tectonic effects. Researchers tend to diverge on whether climate or tectonics is the major
driving force in a given landscape. In an area of constant uplift, Grujie (et al., 2006) revealed that
climate-induced decreases in erosion rates caused the upli ft and preservation of a
paleolandscape. In a separate study of deep tectonic processes, Rogers (et al., 2002) proposed
uplift of a large- scale plateau surface occurred as an upper plate response to the influx of mantle
asthenosphere.
The objective of this project is to describe and map the geology of prominent low-relief
surfaces in the project area. The project area is in the northern San Emigdio Mountains in Southern
California (Figure 1 ). The surfaces are geographically between the uplifted San Emigdio Mesa and
northern San Emigdio Mountain fronts (Photos; Figures 2-3; p. 15). Mapping boundaries range
north to south from California Highway 166, to the Apache Saddle Fire Station (Appendix D). The
anomalous topography was studied through field reconnaissance, identification of the surfaces,
field-geologic mapping, sedimentologica l description, and stereoscope analysis of air photos. It is
proposed that the deposits constitute remnants of a paleolandscape.
1 Regional Geology and Tectonics
The most prominent active structural feature within the study area is the right- lateral San Andreas Fault. The San Andreas Fault System is 1300km long, extending from the Mendocino Fracture Zone to the East Pacific Rise as a complex zone of sheared rock varying from 0.5 to 1km in width (Wallace, 1990). Since 29 Ma, the fault has
produced a highly complex pattern of rock distribution and fault strands (Wallace, 1990).
Within the project area the San Andreas Fault strikes N 60° W in what is known as the
Big Bend portion of its trace (Wallace. 1990). The fault has a documented overall slip rate of 20-30mm/year, but the segment within the project area is considered locked at present
(Irwin, 1990). Other active structures near the San Emigdio Mountains include
(1) the White Wolf Fault, with an undetermined magnitude of left slip and approximately
5km of vertical separation; and (2) the Pleito Fault System, a series of east-west trending, south-dipping thrust faults that are the consequence of north-south shortening in the
Transverse Ranges (Keller et al., 2000; after Rodgers and Chinnery, 1973 and Working
Group on Cali fornia Earthquake Probabilities, 1995).
The San Emigdio Mountains cut across the structural grain of California trending east-west, as part of the southern Coast Ranges (Keller et al., 2000). Since the late
Cenozoic, rocks of the San Emigdio Mountains have been uplifted ~7km to their present elevation of ~2130m (Keller et al., 2000). The San Emigdio Mountains form the boundary between the southern San Joaquin Valley and the Transverse Ranges. As shown by
Keller (et al., 2000), the uplift rate in the northern front of the San Emigdio Range is approximately 2.7-4.3 m/ky, and the locus of active uplift is shifting progressively basinward (northward) toward the San Joaquin Valley. The uplifted
Transverse Ranges block is widening as deformation shifts basinward, causing a series of active and relict mountain fronts to emerge (Keller et al., 2000). Due to relatively shallow
(<3 km) thrust faulting associated with the Pleito Fault System, vertical displacement is transferred into marked surface uplift (Keller et al., 2000).
The northern San Emigdio Mountain fronts are primarily underlain by Bitterwater
Creek Shale, Monterey Shale and Santa Margarita Formation conglomerate (Dean, 2005).
The latest Tertiary and Quaternary deposits (the oldest being Pliocene San Joaquin
Formation) found at the mountain fronts consist predominantly of sandstone and j A conglomerate beds with clasts derived from older rocks found in the adjacent mountain block (Keller et al., 2000). Formative geology of the San Emigdio Mountains includes igneous and metamorphic rocks that are overlain on the northern flank of the range by thick Cenozoic strata (Tulare Formation) (Keller et al., 2000).
3 Materials and Methods
Field reconnaissance of the study area was performed prior to mapping hy traveling along Cerro Noroeste Road, north of Apache Saddle. This was done to assess the regional extent of low-relief surfaces legally accessible on foot. USGS-NAPP infrared aerial photographs (Project Designation 1884; images 51-198. dated 6-11-1989; and Project Designation 1892; images 173-189, dated 6-18-1989) of the San Emigdio
Mountains, San Emigdio Mesa, Elkhorn Plain and southern San Joaquin Valley were used to evaluate the geographic extent of low-relief surfaces. Aerial photographs were studied while field mapping. Reconnaissance results indicated that the area most suitable for study is between California Highway 166 and the Apache Saddle Fire Station.
Quaternary surfaces within the study area were mapped on four USGS 7.5 minute-series (1:24000 seale) topographic maps, enlarged 200%. The topographic maps are the Ballinger Canyon, Santiago Creek, Apache Canyon and Sawmill Mountain
Quadrangles, all having 40-foot topographic contour lines. Field mapping was confirmed, either by up-close scrutinization of the surfaces, or by examining the aerial photographs.
On the final maps, boundaries for the Quaternary surfaces indicated by dashed lines were mapped in the field from some distance (<1km) and supported by airphoto evidence. Boundaries drawn in solid ink represent units scrutinized in detail in the field.
After conducting sedimentological or air-phoio examination of the deposits mapped in the field, those interpreted as possible components of a paleolandscape were transferred to the final maps (1:24000 Quads). Quaternary surfaces on the final maps were drawn-in using a 0.20m m line-width MICRON pen. Colored pencils were used to distinguish the surfaces underlain by different lithological map units. Topographic
4 surface area of the deposits was measured using a digital planim eter. Surface area was measured three times and averaged, with the mean taken as the recorded value. Other topographic information tor the surfaces such as geographic trend, and degree of dissection was recorded directly from the maps.
Sedimentological logs were conducted at two locations where the underlying geology of the low-relief surfaces is exposed. Data was recorded shorthand, in a pocket field notebook, and later expanded, as per the method described by Compton (1985). The sedimentology of each deposit, geographic area, associated or adjacent unit, and minimum deposit thickness (where available) were recorded at each exposure. Data gathered for sediments and clasts found within the deposits includes (1) clast/grain size; (2) character of bedding; (3) whether sediments are clast or matrix supported; (4) thickness of beds and lenses; (5) geologic/mineralogical constituents; (6) sorting; (7) rounding/angularity; and (8) fabric. A 10X hand lens was used to observe sediments, and mineral grains within rocks. A hand level was used in conjunction with my eye-height measurement to measure unit thickness. 8m steel and 50m cloth measuring tapes were used in recording unit thickness and clast size. A camera was utilized to photograph exposures for field evidence, and to create a backup dataset to short-hand notes. A rock hammer was used for scale in the photographs, and as a tool for picking and breaking clasts. To observe the hardness of clasts, the rocks were streaked with a pocket-knife blade. An AMSTRAT grain size card was used in recording rounding/angularity and grain sizes of sediments. Grain sizes are delineated within the phi (ф) or metric scale.
5 Results
Lithological Map Units
Unit Qaf consists of sequences of tabula r, disrupted, and lenticular beds that include matrix-supported grav el-boulder beds, cobble-gravel beds, tine gravel-sand beds, and coarse sand-silt beds (see Appendix B; p. 17 tor detailed unit descriptions). Qaf beds arc either matrix-supported or clast-supported, with the largest clasts found in the matrix- supported sequences. The poorly sorted, matrix-supported beds containing gravel and boulders a re interpreted as debris flow deposits (e.g. Ritter (et al., 2002)). Matrix- supported sequences vary in thickness from 27-75cm. Clast-supported sequences occur in lobate lenses or beds 4-21 cm thick. All sediments of Qaf are generally gray to yellow- brown in color, while clasts range from white to dark gray. Most rocks and sediments within Qaf are sub-rounded to angular. Numerous rock types found with Qaf are derived from undifferentiated Tertiary, and pre-Tertiary units that include sedimentary rocks, and igneous and metamorphic rocks forming the San Emigdio Mountains. Several pieces of evidence suggest that Qaf deposits are truncated, mid-upper alluvial fan surfaces, containing a few facies types. Evidence includes the presence of both matrix-supported and clast-supported beds, the degree of clast rounding, the presence of imbricated clasts, and differences in grain size, sorting, bed thickness and bed morphology (Figure 5) (e.g.
Compton (1985)). Compton (1985) noted that debris flow deposits are typically found in the upper fan. Ritter (et al, 2002) has shown that numerous facies types, controlled by fluctuations in the water/sediment ratio, can occur within the same fan or drainage basin under similar geomorphic controls. Facies types found within Qaf include debris flows.
6 dilute debris flows, transitional flow deposits, fluvial boulder bars and fluvial sheet deposits (see Table 1; p.19: Fan Facies Field Criteria).
Unit Qcf is composed of massive, moderately consolidated, matrix-supported gravel and cobble deposits. These deposits are exposed in erosional gulleys and recent slope failures (Photo; Figure 4; p. 16). Matrix sediments are light brown to gray, moderately-well sorted silt to coarse sand. Rocks suspended in the matrix ar e angular to sub-rounded gravel and cobbles 0.3-17cm in diameter. Clasts show poor to moderate sorting. Some large, angular clasts show slight imbrication. All clasts are derived from
Tertiary and pre-Tertiary units that include sedimentary rocks, and igneous and metamorphic rocks forming the San Emigdio Mountains. Field exposures of Qcf are weakly cemented, and exhibit a high degree of physical weathering. Qcf deposits are interpreted as colluvial relict fill and debris flows, deposited by landslides that evacuated colluvial deposits in hollows. Compton (1985) noted that most materials eroded from slopes are redeposited as colluvium, and can be recognized in position by poorly sorted to unsorted texture, and unbedded structure. According to Ritter (et al., 2002) debris flows are gravity-induced rapid mass movements typically generated on steep bedrock slopes with thin colluvial or soil cover. In a California study relating colluvial erosion and deposition in hollows to climate change, Reneau (et al., 1990) claims that landslides in colluvial deposits are the primary source of debris flows in many mountainous areas.
Mapped Land forms
Mapping efforts documented remnants of the low-relief surface inferred to represent a relict landscape. The total area of the low-relief surfaces is 6.24 km 2. In the field, mapping efforts were limited by lack of access and poor exposure. The surfaces
7 depicted on the final map (Appendix D) are those that were best supported by field and air-photo evidence. However, reconnaissance and air-photo evidence suggests that the low-relief surfaces comprising the paleolandscape are more extensive.
■*. ■ í Topographic relief within the boundaries of mapped surfaces is moderate. The maximum relief found for any of the surfaces is 360ft. The minimum relief is <40ft., and the mean value for all of the surfaces is 226.7ft.
Deposits of Qaf between 5600 ft. and 5920 ft. are highly dissected. Qaf is bound or eroded by seven individual streams. Two of the streams are tributaries to Santiago
Creek, and five are tributaries to Quatal Canyon. Streams incising the southern remnants of Qaf have a maximum relief of 900ft. Streams near the northern portion of Qaf that flow within the San Andreas Fault 'Rift Zone', have incised 1200 ft. below the paleolandscape.
To the northwest, the low-relief surfaces distinguishing Cowhead Potrero and Apache
Potrero are moderately dissected. The undifferentiated Quaternary deposits at Cowhead
Potrero are bound by three streams in the north (which drain to Santiago Creek), and dissected by only one stream in the south (a tributary to Quatal Canyon). At Apache
Potrero, a deeply-incised network of four streams draining north to Santiago Creek has removed the Quaternary sediments. To the southwest, seven smaller tributaries to Quatal
Canyon dissect the Apache Potrero sediments, and more of the surface is preserved. For
Cowhead and Apache Potreros, stream networks that boundary the surfaces and drain north toward the San Andreas Fault ‘Rift Zone' have incised as much as 1000 ft. below adjacent paleolandscape surfaces. Streams dissecting the Potreros that drain southwest have incised about 400 ft. below the paleolandscape, across the same horizontal distance.
8 Qcf deposits are poorly preserved on the northeast side of Cerro Noroeste Road.
For example, the deposits of Qcf above Ballinger Canyon are dissected hy three
southwest-flowing streams. Relief between channels of streams di ssecting Qcf, and
surfaces underlain hy Qcf is about 400 ft. The deposit located farthest to the northwest
on the map (near Benchmark elevation 4375) is an undissected, closed-drainage low-
relief surface that is assumed to be Qcf based on its topographic position.
The Quaternary deposits underlying the paleolandscape surfaces trend northwest
along a linear trace that is approximately 17.4km in length. The altitude of the entire
surface is within 4200-5800 ft. Over most of the surface area (with the exception of
some of Qaf). the deposits generally lack dense, woody vegetation and mature trees.
Discussion
Prior to mapping and sedimentologic evaluation, it was thought that the low-relief
surfaces preserved in the project area may constitute a once-contiguous alluvia l surface.
In a previous study using hypsometric analysis. Dean (2005) concluded that similarities
between hypsometric curves for three study areas in the Elkhorn Plain and San Emigdio
Mesa showed that each contained remnants of a once-contiguous low-relief alluvial
surface. The results presented in this paper generally concur with Dean's hypothesis.
The surfaces evaluated herein are interpreted as belonging to the same paleolandscape.
The distinction that must be made is, instead of one contiguous surface of alluvium, Qaf and Qcf deposits represent *morphostratigraphica!ly distinct elements of the same paleo fluvial level.
Qaf and Qcf contain many clasts having a similar source, derived mostly from the
San Emigdio Mountain block. Qaf and Qcf deposits were formed by the erosion and
*morphostratigraphy = a combination of landform morphology, map pattern, and sedimentol ogy 9 deposition of mountain block rocks following earlier stages of uplift. The presence of remnants of Qaf and Qcf at high elevations suggests that the deposits were emplaced at lower elevations near active mountain fronts (Pleistocene or younger). Subsequent uplift must have brought the surfaces to their present elevations, before they could be completely denuded by stream incision. Qaf and Qcf are well-preserved only where stream incision is not highly developed. Stream incision and denudation are more developed at higher elevations (south extent of project area). Therefore most of the relict surfaces lie below 5900ft. in elevation.
Due to a series of thrust faults (possibly connected at a basal decollement), Keller
(et al., 2000) has shown that the uplifted block of the San Emigdios is widening as the locus of uplift shifts northward, causing a series of active and relict mountain fronts to emerge. Based on their *morphostratigraphy, Qaf and Qcf probably formed near the locus of an older range front, before deformation propagated northward. Qaf is interpreted as an alluvial fan surface that formed proximal to an older range front, at the piedmont of the San Emigdio Mountains.
Debris flow events are considered common in semiarid, mountainous and vegetated chaparral regions such as California (Ritter et a l, 2002). Colluvial deposits in hollows are the predominant source of debris flows in many mountainous areas (Reneau et af, 1990). Because of their morphologic character (texture and structure) and location in a mountainous region having a long history of tectonic activity and episodic, intense storms, Qcf deposits are interpreted as debris flows that were emplaced primarily by the evacuation of colluvium-filled hollows. Earlier in the Quaternary period, colluvium- filled hollows likely existed in foothills of the San Emigdio Mountain piedmont. Once
10 scoured-out, colluvial debris from hollows could be transported down slope and deposited more distal to the mountain peaks (than Qaf), but within the same paleo base- level as the active fans.
Conclusions
Previous reconnaissance and air-photo observations sparked interest in prominent low-relief surfaces scattered throughout dissected, mountainous topography in the Big
Bend region of the San Andreas Fault. The topographic expression of the surfaces, coupled with their preservation in a region characterized by rapid and complex tectonic deformation suggested that they may be recently uplifted elements of a once-contiguous landscape. Due to similarities among several hypsometric curves for study sites in the region. Dean (2005) inferred that they may contain remnants of a once-contiguous surface of alluvium. Mapping and sedimentological studies presented in this paper show that the accessible low-relief surfaces represent morphostratigraphically different
Quaternary units, originally deposited at the same paleofluvial level. Qaf are alluvial fan deposits that contain debris flow facies. The Quaternary fan probably drained eroded materials from the uplifting San Emigdio Mountains near an older, active range front.
Qcf represents debris flows / relict colluvial fill that flowed from the mountain piedmont to the low-relief valley surface beneath an older, active range front. These colluvial deposits were most likely derived from colluvial hollows, evacuated during intense storms. In this region of marked tectonic activity, it is difficult to assert whether tectonics or the paleoclimate was the principal cause in preserving the relict surfaces.
Ritter (et al., 2002) has suggested that debris flow facies on fans can be indicators of past climatic instability. Reneau (et al., 1990) has shown that accelerated cycles of intense
11 storms during the Pleistocene-Holocene transition likely caused widespread landsliding from colluvial hollows. But given the rapid and dynamic nature of tectonics in this region, further study is required to deduce climate vs. tectonic controls.
12 References
Brown, R.D. Jr., 1990. Quaternary deformation. In Wallace, R., ed.. The San Andreas fault system, California. United States Government Printing Office, Washington, D.C., p.83-113.
Compton, R.R. 1985. Geology in the field. John Wiley & Sons, Inc., Hoboken, NJ,
Dean, D.M. 2005. Comparative hypsometry of the Elkhom Plain and San Emigdio Mountains, California. Senior Project. California Polytechnic State University, San Luis Obispo.
Grujic, D.. I. Coutand, B. Bookhagen, S. Bonnet, A. Blythe, and C. Duncan. 2006. Climatic forcing of erosion, landscape and tectonics in the Bhutan Himalayas. Geology 34 10:801-804.
Irwin. W.P., 1990, Geology and plate-tectonic development. In Wallace, R., ed., The San Andreas fault system, California. United States Government Printing Office, Washington, D.C., p.61-80.
Keller. E.A., D.B. Seaver, D.L. Laduzinsky, D.L. Johnson, and T.L. Ku. 2000. Tectonic geomorphology of active folding over buried reverse faults: San Emigdio Mountain Front , Southern San Joaquin Valley, California. GSA Bulletin 112: 86-97.
Reneau, S.L., W.E. Dietrich, D.J. Donahue, A.J.T. Jull, and M. Rubin. 1990. Late Quaternary history of colluvial deposition and erosion in hollows , Central California Coast Ranges. Geological Society of America Bulletin 102: 969-982.
Ritter, D.F., R.C. Kochel, and J.R. Miller. 1995. Process geomorphology 3 rd Ed.: W.C. Brown Publishers, Dubuque, IA, 539 pp.
Rogers, R.D., H. Karason, and R.D. van der Hilst. 2002. Epeirogenic uplift above a detached slab in northern Сentra l America. Geology 30 11: 1031 -1034.
13 APPENDIX A. Figures
SAF=San Andreas Fault BB=Big Bend Region
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Image courtesy oř the U.S. Geological Survev ■© 2004 Microsoft Corporat ion Terms of Use Privacy Statement
1. Site Map. Maps from Keller (et al., 2000) and USGS Terra Server (2004).
14 APPENDIX A. Figures
Figure 2. Low-relief surface in foreground preserved in dissected mountainous topography. Photo courtesy of A. F. Garcia
Figure 3. Barn situated on a low-relief surface in the San Emigdio Mesa area. Photo courtesy of A. F. Garcia
APPENDIX A. Figures
15 APPENDIX A. Figures
Figure 4. Qcf deposits underlying a low-relief surface; exposed in a gu lley.
Figure 5 . Lower portion of a Qaf (fan) sequence approx. 35m thick .
16 APPENDIX В MAP UNIT DESCRIPTIONS Map Unit Sedimentology
Qaf Quaternary alluvial fan deposits. Moderately dissected, truncated fan surfaces underlain by alluvium having a minimum thickness of 2.85m. This description is based on an exposure at an erosion surface 0.8km SE of Santiago Creek (in the San Andreas Fault Rift Zone), 200m N of Cerro Noroeste Road, and 2.75km NW of Apache Saddle Fire Station. Deposits locally overlie Tp Tu along unconformable contacts. Qaf consists of tabular, disrupted and lenticular beds that include matrix-supported gravel- boulder beds, cobble-gravel beds, fine gravel-sand beds, and coarse sand-silt beds. Qaf beds are either matrix supported or clast supported, with the largest clasts found in matrix supported sequences (debris flows deposits). Matrix supported sequences locally vary in thickness from 27-75cm. Gray to yellow-brown matrix sediments are composed of silt, and very fine to coarse sand, with diameters from 4.0 phi to <1 cm. Sediments are subrounded to angular. Silt and sand beds are moderately to poorly sorted. Composition of matrix sediments includes quartzose, feldspathic, and biotite- bearing grains. Clasts in the matrix are gravel, cobbles and boulders with diameters from 2cm-0.75m. Clasts are sub- rounded to angular, and poorly sorted. Gravel-boulder clasts are composed of dark brown sandstone and siltstone, tan to gray quartzose and feldspathic sandstone, quartzite, and grey metamorphic rocks (unit Tp Tu). Clast supported sequences occur in lenses (some lobate) or beds 4-21 cm thick. Grains and clasts are composed of dark gray sand and gravel, 3.5 phi-3cm in diameter. Sand in clast supported beds are round to sub-angular, gravel clasts arc sub-rounded to angular. Sand is well-sorted and gravel is poorly sorted. Sand includes quartzose, feldspathic and biotite-bearing grains. Gravel includes siltstone, quartzose sandstone, quartzite, and grey metamorphic rocks (unit TpTu). Gravels show moderate imbrication.
17 APPENDIX В MAP UNIT DESCRIPTIONS Sendimentology
Qcf Quaternary colluvial relict fill. Moderately dissected colluvial fill and debris flow deposits. Poor exposure and limited access precludes detailed measurements and descriptions. This description is based on an exposure in the Los Padres National Forest, 3-50m east of Cerro Noroeste Road, approximately 15.5 km SE of California Hwy. 166. Deposit locally overlies Tp Tu at unconformable contacts. Qcf is composed of massive, moderately consolidated, matrix-supported gravel and cobble deposits. Matrix sediments locally consist of light brown to grey, bimodal silty very fine to coarse sand. Sediments are moderately to well sorted, with grain sizes from 3.5 to 1.0 phi. Matrix constituents are predominantly quartzose and feldspathic, with lesser amounts of biotite, hornblende and vermiculite. Rocks suspended in the matrix consist of gravel and cobbles derived from unit Tp Tu. Gravel and cobbles are angular to sub-rounded, moderately to poorly sorted, with diameters from 0.3-17cm. Some large clasts show moderate imbrication.
TpTu Undifferentiated Tertiary and pre-Tertiary sedimentary and crystalline basement rocks.
18 APPENDIX C. Tables
Table 1 Morphologic and Sedimentologi c Field Criteria for Distinguishing Facies Types on Alluvial Fans
Facies Types Morphology Depositional Relief (m) Texture and Stratification Characteristics of Clast Fabric
Debris flow (D1) Lobate to digitate High (0.8-1.5) Matrix rich Elongate clasts oriented parallel to flow Narrow Matrix supported forming a push fabnc Steep front/flanks Poorly sorted Flat tops Stratification absent Pressure ridges
Dilute debris flow(D2) Thin, lobate Moderate (0.3-0.5) Matrix rich None observed Broad, flat top Matrix supported Gentle lobe fronts Poorly sorted Stratification absent
Transitional flow dep. (T1) Stacked lobes High (0.5-1.5) Clast support Collapse packing Broad small mounds Sand matrix w/increasing depth Collapse depressions Moderately sorted Stratification present
Fluvial boulder bar and lobes (S1) Linear bars to Moderate-High (0.5-0.8) No Matrix Imbrication transverse lobes Clast support Front to tail Sorting
Fluvial longitudinal bar (S2) Linear bars Moderate (0.2-0.5) Clast support Strong imbrication Sand matrix w/increasing depth Poorly sorted
Fluvial sheet deposits (S3) Broad and flat Low (~0.1) Clast support Weak imbrication Some fan shaped Little matrix (sandy)
Subdued bar and Well stratified swale forms Moderate sorting Normal grading in some strata
** From Ritter (et al., 2002). Originally by Wells and Harvey (1987).
19 APPENDIX D.
Surficial geologic pma of the Apache Saddle/Bitter Creek National Wildlife Sanctuary environs San Emigdio Mountains Kern and Ventura Counties Сalifomia
Paul G. Lavelle
Earth and Soil Sciences Department California Polytechnic State University
20